Increasingly, a multiple number of sand cores are used in a built-up core assembly in the casting of automotive parts. Heretofore, cores have been designed to fit one upon another when being used in a built-up assembly and have typically rested loosely keyed together. This mode was acceptable because automotive castings were generally designed with sufficient bulk that the ultimate casting tolerated some limited inaccuracy from core shift during metal pouring. However, with modern restrictions being placed on automotive components as to weight, castings must be designed with maximum leanness and thus core shifting or inaccuracies cannot be tolerated.
The prior art has in certain instances locked core assemblies together in critical requirement type casting by the use of principally two modes. One mode has involved pasting the core components together and then subjecting the assembled cores to an oven drying operation for completing the attachment. This method requires an extra step with respect to dipping the core components in a paste tank and, of course, the subsequent oven treatment; the cost of oven equipment used to dry the paste is undesirable. These steps increase manpower and time requirements.
The other mode has involved use of discardable bolts and nuts to clamp the sand core assembly together. Bolt openings are typically formed in the assembly to extend entirely therethrough. This system is disadvantageous because the bolts must be removed after the casting is produced, which is quite difficult and arduous when carrying out core removal. Frequently, the bolts are not removed because they have become fused with the casting. Scrap rates are increased and material handling is excessive.